This invention lies in the field of gas flaring systems. More particularly, it concerns flares in which waste gases are flared and in which steam is used for injection into the flame zone for the purpose of smokeless combustion of the gases.
Still more particularly, this invention is concerned with the protection of the steam injection parts from excessive heat due to the maintenance gas flow, when waste gases are not being flared.
The art of smokeless flare burning of smoke prone gases, through the injection of steam in the conventional manner, to the burning zone of the flare, is now well known. For the portion of the year when ambient temperature is higher than the freezing point of water there is little difficulty involved in flare operations. However, when the ambient temperature falls to or below freezing, there is considerable difficulty.
The difficulty arises because, for a very large percentage of the time, the flare is either in standby condition, for emergency flaring, or is discharging and burning gases at a minimal rate, which may be of the order of 1% of design flow capacity. This condition of gas burning, even though it is a small portion of the flare capacity, it is still productive of enough heat to very seriously damage the steam injection parts, unless there is constant flow of a coolant medium through and from the steam injection parts.
A typical coolant medium is steam, and when the weather is mild, cooling by steam flow is quite satisfactory. Although the quantity of steam flowing is quite small, because the cost of steam is so great, such flow is expensive. Also, in cold weather, a large portion of the steam condenses to water, to be sprayed at random over the critical flare discharge areas. At very low temperatures, ice forms in or near the flare discharge areas to partially or completely block the flared gas passages to the atmosphere. This can bring about a condition of extreme emergency in the process operations, where flare venting of emergency relieved gases demands instant and unobstructed gas flow to the atmosphere.
There is also another source of water which may ultimately freeze in and on the flare. This comes from the large capacity steam line from the source of steam, to a control point at the base of the flare. The steam line, which is typically hundreds of feet long, and is either at no flow or very small flow at the time the flare is on standby, is subject to heat loss despite insulation. At a time when the control means calls for steam, and flow to the flare from the control point begins, the flow is initially all the accumulated condensate, to be followed by steam, after the water is cleared out. Then there is additional water which has accumulated in low areas of the steam line, which flows as slugs, on arrival at the steam line up the flare. However water may be delivered to the flare, the freezing hazard is present and it demands solution in point of sources of water, at or near to the burning zone of the flare, when the weather can cause freezing of the water.